Vending machines in Montgomery County schools will remain dark after the last bell of the school day rings, keeping students from loading up on snacks and treats before they head home.

A group of Montgomery parents successfully worked with school system officials to keep vending machines turned off for 30 minutes after classes end for the day. Vending machines currently turn on when school ends.

“The students at [Montgomery County schools] will no longer have easy access to sugary sodas, candy and other unhealthy items immediately after school,” said Lindsey Parsons, co-founder of Real Food for Kids — Montgomery. “This will no doubt have a positive effect on many children.”

The policy applies only to vending machines carrying food that doesn’t meet the school system’s wellness guidelines.

The U.S. Department of Agriculture recently approved new, tighter nutrition rules for snacks in public schools. The new rules require vending machines to stay off until 30 minutes after the school day ends. But the guidelines don’t go into effect until the 2014-15 school year, which means the change in Montgomery will happen a year earlier than required.

Vending machine timers should all be adjusted before school starts at the end of August, Superintendent Joshua P. Starr said in a letter addressing the policy.

“The Montgomery County Board of Education and I continue to support nutritional requirements that pertain to foods and beverages available to students from midnight until the end of the school day as outlined in regulation,” Starr’s letter said.

Real Food for Kids — Montgomery organized last fall, aiming to raise nutritional standards for food available in county schools, and members have worked with the district to test out healthier vending and cafeteria snacks at Takoma Park Middle School. Parsons said the pilot program at Takoma Park will replace snacks containing certain additives and dyes with healthier selections and will ban artificial sweeteners such as aspartame.

The group also seeks nutritional reform beyond the county. Although Parsons said the 30-minute rule is a good start, the group wants to ban all vending machines from selling foods that don’t match school system’s wellness guidelines. The organization recently applied for a grant to develop such legislation statewide.

“We don’t want those machines at schools, period,” Parsons said. “We know students are at school for longer than 30 minutes after the day ends.”

The group is affiliated with a similar advocacy organization that started in Fairfax and has successfully pushed Fairfax County public schools to remove foods containing artificial preservatives, dyes and other additives from being served to students. Both the Fairfax and Montgomery parent groups have been seeking changes that are stricter than the USDA guidelines, with an emphasis on fresher, healthier foods in schools.

With roughly one-third of U.S. children categorized as overweight or obese, the Obama administration has been driving new school food rules nationwide, changing the portion sizes of lunches and regulating snack foods for schools that had lax rules. The national guidelines for snack foods in schools, approved in June, generally require snacks to have fewer than 200 calories per serving, with less than 35 percent of the food’s weight coming from sugar. They also limit the calories for sweetened beverages.